Esterification of cellulose



Patented, Mar. 3, 1936 UNITED STATES- PATENT OFFICE ESTERIFICATION or CELLULOSE Joseph F. Haslrins, Wilmington, DeL, assig'nor to E. I. du Pont de Nemours & Company, Wilminim No Drawing.

11, Del., a corporation of Delaware Application June 24, 1932, Serial No. 619,120

26 Claims. (01. 260-401) This invention relates to the preparation of the acid halide and some or the tertiary amine to form a ketene and by the polymerization of theketene to form colored resins which are hard to remove. It is also known that cellulose may be esterifled by the action of acid anhydrides in the presence of tertiary amines and, in particular,

5 in the presence of pyridine. This reaction is,

however, unsatisfactory in that the esterification .is extremely slow and in that the products are'in general of poor solubility.

In the copending application of Haskins and zofSchulze, Serial Number 422,549, filed January 22,

1930, Patent No. 1,967,405, July 24, 1934, it has been disclosed that acid anhydrides will esterify cellulose readily in the presence of tertiary amines provided appropriate catalysts are used. This reaction, because oi the non-formation or less formation 01' objectionable by-products, produces a more easily purified product. This process is to be preferred to the process wherein acid chlorides are used except that in some cases the acid chloride is more conveniently or more economi cally prepared than the acid anhydride. In my copending case Serial Number 553,006, filed July 24 1931, there is described the production of an esteriiying solution by the interaction of organic acid chlorides with organic carboxylic 1 acids in the presence of tertiary amines. The present case is an improvement upon the invention disclosed in the last-identified copending case.

40 It is an object of the invention to esterify cellulose in' particular and carbohydrates in general. The reaction is applicable to various forms of pure. celluloses including the alpha, beta, and gamma forms, to modified celluloses which still retain a reactive hydroxyl group such as hydrocelluloses and the partially esterified or etherifled cellulose esters and ethers. Among the carbohydrates to which the process may be applied are the polyoses in general and starch in particular.

The invention will be described in its application to the esterification of cellulose.

The objects 01 the invention are accomplished, generally speaking, by reacting cellulose with a bath made by mixing a fatty acid, a tertiary 56 amine such aspyridinaand its homologs, land phosgene in an inert diluent. The following description and examples are exemplary and are not to be construed as limitative.

' Example I Ten (10) parts of pyridine and 9.4 parts of propionic acid were added to 60 parts of dioxane.

This solution was warmed slightly and phosgene" was passed into it until it became acid to methyl orange. Carbon dioxide was allowed to escape through benzene to dissolve any phosgene which it contained. The mixture was then heated to'expel more carbon dioxide. When the carbon dioxide ebullition had substantially ceased, enough pyridine was added to make the solution basic to methyl orange and about 5 parts excess in addition. This solution was then mixed with about 1 part of alpha cellulose (cotton linters pulp). The whole was placed'in a tube which was sealed and heated at 1103 C. with 20 agitation until solution was complete. This required about ten hours.

After the reaction was completed there were two layers present in the tube, the lower layer consisting essentially of pyridine hydrochloride and the upper layer consisting of a solution of cellulose propionate in dioxane. Upon cooling, the lower layer solidified and the upper layer was poured into water with stirring, precipitating the cellulose ester. The precipitate was washed with 30 water and dried and proved to be a cellulose tripropionate soluble in chloroform, acetone, pyridine anddioxane. p

Example [I To about 60 parts of chlorobenzene were added 35 about 10 parts of pyridine, about 3.8 parts of acetic acid and about 6.5 parts of iso-valeric acid. The passing of phosgene into the mixture and the remainder of the experiment were carried out substantially as in Example I except that the re- 4 action product was coagulated in a mixture of waterand methyl alcohol. The ester proved to be a mixed cellulose acetate iso-valerate soluble in chlorofrom, acetone, pyridine, and dioxane.

The diluents listed in the above examples are 4 dioxane and chlorobenzene but many other diluents are useful. Among the useful diluents benzene, amylf. acetate, and nitrobenzene may be named as of particular value. These compounds do not by any means exhaust the list, which con- 56 tains a great many compounds, but-serve to illus-' trate the fact that the character of the diluent is not limited to any particular class oi compounds. The diluent may be omitted from the reaction mixture but its omission is not desirable formed and was 10 contaminated by by-products.

of the invention are in part apparent and in part because of the formation of colored by-products.

Other acids, for example, capric, lauric, and stearic, may be used but with them the reaction goes more slowly. Acids having from two to eight carbon atoms are in general those giving the preferred results in our process.

The range of temperatures at which the reaction can be carried out is extremely broad and it is neithernecessary nor desirable to state upper and lower limits ther of. As the temperature at which the reaction akes place afiects the solubility of the product, it is advantageous to use temperatures between about80 and about 150 C. when a product having good solubility is desired. The temperature not being critical as to actual operativeness of the process, determinationof the maximum and theminimum temperatureswhich give optimum results is best left to the chemist to select in view of the characteristics he desires in the product.

The examples were carried out at elevated pressures but this is not essential. The reaction can be carried out at ordinary or at reduced pressures although the volatility of certain ingredients of the reaction makes the latter less easy to manipulate.

An advantage of this invention over prior processes lies in the low cost of the reactants. An-

other advantage is in that the by-products of the reaction between the esterifying materials are gaseous and pass off leaving a solution un- Other advantages set forth elsewhere in the specification.

. excess to make the solution basic to methyl orange, and treating about 1 part of cellulose with the solution at a temperature of about 110 C. and at elevated pressure until solution is substantially complete.

2. The method of esteriiying cellulose which comprises mixing pyridine and propionic acid with dioxane, passing phosgeneinto the solution at slightly elevated temperature until it becomes acid to methyl orange, heating to expel carbon dioxide, adding pyridine in slight excess to make vthe solution basic to methyl orange, and treating cellulose with the solution at a temperature of about 110 C. and at elevated pressure until solution is substantially complete.

3. The method of esterifying cellulose which comprises mixing pyridine and propionic acid with dioxane, passing phosgene into the solution at slightly elevated temperature until it becomes acid to methyl orange, heating to expel carbon dioxide, adding pyridine to make the solution basic to methyl orange and adding cellulose to the solution and heating to a temperature of about 110 C. in a closed vessel.

4. The method of esterifying cellulose which comprises mixing pyridine and propionic acid with an inert diluent, passing phosgene into the solution at slightly elevated temperature until it becomes acid to methyl orange, expelling carbon dioxide, adding pyridine to make the solution basic to methyl orange, adding cellulose to the solution and heating to a temperature of about 110 C. in a closed vessel.

5. The method of esterifying cellulose which comprises mixing pyridine and a fatty acid with an inert diluent, passing phosgene into the solution until it becomes acid to methyl orange, adding pyridine to make the solution basic to methyl orange, adding cellulose to the solution and heating in a closed vessel until solution is substantially complete.

6. The method of. esterifying cellulose which comprises mixing pyridine, phosgene, and a fatty acid with an inert diluent in proportions of phosgene to the other ingredients such that the solution will be'acid to methyl orange, adding pyridine to make the solution basic to methyl orange, and heating cellulose in the solution in a closed vessel until solution is substantially complete.

'7. The method of esterifying cellulose which comprises reacting pyridine, phosgene, and an aliphatic monocarboxylic acid in an inert diluent and treatingcellulose with the solution at elevated temperature. i

8. The method of esterifying cellulose which comprises mixing about 10 parts of pyridine, about 3.8 parts of acetic acid, and about 6.5 parts of iso-valeric acid with about 60 parts of chlorobenzene, passing phosgene into the solution "at slightly elevated temperature until the solution becomes acid to methyl orange, heating to expel until the solution becomes-acid to methyl orange,

heating to expel carbon dioxide, adding pyridine until the solution is basic to methyl orange, and treating cellulose with the solution at a temperature of about 110 C. at elevated pressure.

10. The method of esterifying cellulose which comprises mixing pyridine, acetic acid, and isovaleric acid with an inert diluent, passing phosgene into the solution until the solution becomes acid to methyl orange, expelling carbon dioxide, adding pyridine until the solution is basic to methyl orange, and treating cellulose with the solution at elevated temperature and elevated pressure.

11. The method of esterifyingcellulose which comprises mixing phosgene, pyridine, acetic acid, and iso-valeric acid with an inert diluent in proportions acid to methyl orange, expelling carbon dioxide, adding pyridine until the solution is basic to methyl orange, and treating cellulose with the solution at elevated temperature and elevated pressure.

12. The method of esterifylng cellulose which comprises mixing phosgene, pyridine, acetic acid,

and iso-valeric acid in proportions acid to methyl orange, adding pyridine until the solution is basic to methyl orange, and esterifying cellulose with the solution.

13. The method of esterifying cellulose which comprises mixing phosgene, pyridine, a fatty acid, and a diiferent fatty acid in proportions acid to methyl orange. adding pyridine until the solution g I aces-14o .3 is basic to methyl orange, and esterifying celluclosed vessel until solution is substantially comlose with the solution. plete.

14. The method of esterifying cellulose which comprises mixing phosgene, pyridine, an aliphatic monocarboxylic acid and a diilerent aliphatic monocarboxylic acid, adding pyridine until the solution is basic to methyl orange, and esterifying cellulose'with the solution.

15. The method of esterifying cellulose which comprises mixing phosgene and pyridine with a plurality of fatty acids, hnd esterii'ying cellulose with the solution.

16. The method of esterlfying cellulose which comprises reacting cellulose with the contents of a hath made by mixing an aliphatic monocarboiwlic acid, phosgene, and pyridine.

17. In a process of esterifying cellulose the step which comprises adding phosgene to a fatty acid and pyridine.

18. The method of esterifying cellulose which comprises reacting Pyridine, phosgene, and an aliphatic monocarboxylic acid having from two to eight carbon atoms in an inert diluent, and treating cellulose with the solution at elevated temperature.

19. The method of esterifying cellulose which comprises mixing pyridine, phosgene, and a fatty acid having from two to eight carbon atoms with an inert diluent in proportions of pho'sgene to'the other ingredients such that the solution will be acid to methyl orange, adding pyridine to make the solution basic to methyl orange, and heating cellulose in the solution in a closed vessel until solution is substantially complete.

20. The method of esterifying cellulose which comprises mixing pyridine and a fatty acid having from two to eight carbon atoms with an inert diluent, passing phosgene into the solution until it becomes acid to methyl orange, adding pyridine to make the solution basic to methyl orange, adding cellulose to the solution and heating in a 21. The method of esterifying cellulose which comprises mixing phosgene, pyridine. a fatty acid having from two to eight carbonatoms, and a different fatty acid having from two to eight carbon atoms in proportions acid to methyl orange, adding pyridine until the solution is basic to methyl orange, and esterifying cellulose with the solution. I

22. The method of esterlfying cellulose which comprises mixing phosgene, pyridine, an aliphatic monocarboxylic acid having from two to eight carbon atoms, and a difierent aliphatic monocarbozvllc acid having from two to eight carbon atoms, adding pyridine until the solution is basic to methyl orange, and esterifying cellulose with the solution.

23. The method of esterifying carbohydrates which comprises reacting a carbohydrate with the contents of a bath made by mixing an organic carboxylic acid, phosgene, and pyridine.

24. In a process of preparing a bathfor the esteriflcation of cellulose the step which comprises reacting phosgene, fatty acids, and pyridine in an inert diluent.

25. In the preparation of aliphatic monocar= boxylic esters of carbohydrates the steps which 'comprise mixing pyridine with acid which is to be reacted with the carbohydrate, adding phosgene, and allowing the phosgene to react with th acid. a 26. In the preparation of aliphatic monocarboxylic esters of carbohydrates the steps which comprise mixing p dine with acid which is to be reacted with the carbohydrate, adding phosgene,

and allowing the phosgene to react with the acid.

said reaction being carried out in the presence of a diluent- -.JOBEPI-I nrmsxms. 4o 

